engine: implement small Message Rewrite Facitility that allows to run mods that directly write internal GoldSrc messages

Documentation/bug-compatibility.md

@@ -13,3 +13,4 @@ When `-bugcomp` is specified with argument, it interpreted as flags separated wi
 | Flag    | Description | Games that require this flag |
 | ------- | ----------- | ---------------------------- |
 | `peoei` | Reverts `pfnPEntityOfEntIndex` behavior to GoldSrc, where it returns NULL for last player due to incorrect player index comparison | * Counter-Strike: Condition Zero - Deleted Scenes |
+| `gsmrf` | Rewrites message at the moment when Game DLL attempts to write an internal engine message, usually specific to GoldSrc protocol. Right now only supports `svc_spawnstaticsound`, more messages added by request. | * MetaMod/AMXModX based mods |

engine/common/common.h

@@ -275,6 +275,10 @@ typedef enum bugcomp_e
 {
 	// reverts fix for pfnPEntityOfEntIndex for bug compatibility with GoldSrc
 	BUGCOMP_PENTITYOFENTINDEX_FLAG = BIT( 0 ),
+
+	// rewrites mod's attempts to write GoldSrc-specific messages into Xash protocol
+	// (new wrappers are added by request)
+	BUGCOMP_MESSAGE_REWRITE_FACILITY_FLAG = BIT( 1 ),
 } bugcomp_t;
 
 typedef struct host_parm_s

engine/common/host.c

@@ -75,6 +75,7 @@ typedef struct feature_message_s
 static feature_message_t bugcomp_features[] =
 {
 { BUGCOMP_PENTITYOFENTINDEX_FLAG, "pfnPEntityOfEntIndex bugfix revert", "peoei" },
+{ BUGCOMP_MESSAGE_REWRITE_FACILITY_FLAG, "GoldSrc Message Rewrite Facility", "gsmrf" },
 };
 
 static feature_message_t engine_features[] =

engine/server/server.h

@@ -329,6 +329,8 @@ typedef struct
 	int		msg_realsize;		// left in bytes
 	int		msg_index;		// for debug messages
 	int		msg_dest;			// msg destination ( MSG_ONE, MSG_ALL etc )
+	int     msg_rewrite_index;
+	int     msg_rewrite_pos;
 	qboolean		msg_started;		// to avoid recursive included messages
 	edict_t		*msg_ent;			// user message member entity
 	vec3_t		msg_org;			// user message member origin

engine/server/sv_game.c

@@ -2501,6 +2501,62 @@ int GAME_EXPORT pfnDecalIndex( const char *m )
 	return -1;
 }
 
+static int SV_CanRewriteMessage( int msg_num )
+{
+	// feature is disabled
+	if( !FBitSet( host.bugcomp, BUGCOMP_MESSAGE_REWRITE_FACILITY_FLAG ))
+		return 0;
+
+	switch( msg_num )
+	{
+	case svc_goldsrc_spawnstaticsound:
+		return svc_sound;
+	}
+
+	return 0;
+}
+
+static qboolean SV_RewriteMessage( void )
+{
+	vec3_t origin;
+	const char *sample = NULL;
+	float vol, attn;
+	int ent, pitch, flags, idx;
+	int cmd;
+
+	MSG_SeekToBit( &sv.multicast, svgame.msg_rewrite_pos, SEEK_SET );
+
+	cmd = MSG_ReadCmd( &sv.multicast, NS_SERVER );
+
+	switch( cmd )
+	{
+	case svc_goldsrc_spawnstaticsound:
+		MSG_ReadVec3Coord( &sv.multicast, origin );
+		idx   = MSG_ReadShort( &sv.multicast );
+		vol   = MSG_ReadByte( &sv.multicast );
+		attn  = MSG_ReadByte( &sv.multicast ) / 64.0f;
+		ent   = MSG_ReadShort( &sv.multicast );
+		pitch = MSG_ReadByte( &sv.multicast );
+		flags = MSG_ReadByte( &sv.multicast );
+
+		if( FBitSet( flags, SND_SENTENCE ))
+			sample = va( "!%i", idx );
+		else if( idx >= 0 && idx < MAX_SOUNDS )
+			sample = sv.sound_precache[idx];
+
+		if( !COM_CheckString( sample ))
+		{
+			Con_Printf( S_ERROR "%s: unrecognized sample in svc_spawnstaticsound, index %d, flags 0x%x\n", __func__, idx, flags );
+			return false;
+		}
+
+		MSG_SeekToBit( &sv.multicast, svgame.msg_rewrite_pos, SEEK_SET );
+		return SV_BuildSoundMsg( &sv.multicast, EDICT_NUM( ent ), CHAN_STATIC, sample, vol, attn, flags, pitch, origin );
+	}
+
+	return false;
+}
+
 /*
 =============
 pfnMessageBegin
@@ -2518,10 +2574,24 @@ static void GAME_EXPORT pfnMessageBegin( int msg_dest, int msg_num, const float
 	// check range
 	msg_num = bound( svc_bad, msg_num, 255 );
 
+	svgame.msg_rewrite_index = 0;
+	svgame.msg_rewrite_pos = 0;
+
 	if( msg_num <= svc_lastmsg )
 	{
-		svgame.msg_index = -msg_num; // this is a system message
-		svgame.msg_name = svc_strings[msg_num];
+		// check if we should rewrite this message into something else...
+		if( SV_CanRewriteMessage( msg_num ))
+		{
+			svgame.msg_index = -SV_CanRewriteMessage( msg_num );
+			svgame.msg_name = svc_goldsrc_strings[msg_num] ? svc_goldsrc_strings[msg_num] : svc_strings[msg_num];
+			svgame.msg_rewrite_index = msg_num;
+			svgame.msg_rewrite_pos = MSG_TellBit( &sv.multicast );
+		}
+		else
+		{
+			svgame.msg_index = -msg_num; // this is a system message
+			svgame.msg_name = svc_strings[msg_num];
+		}
 
 		if( msg_num == svc_temp_entity )
 			iSize = -1; // temp entity have variable size
@@ -2596,6 +2666,25 @@ static void GAME_EXPORT pfnMessageEnd( void )
 		return;
 	}
 
+	if( svgame.msg_rewrite_index != 0 )
+	{
+		if( SV_RewriteMessage( ))
+		{
+			if( MSG_CheckOverflow( &sv.multicast ))
+			{
+				Con_Printf( S_ERROR "MessageEnd: %s has overflow multicast buffer (post-rewrite)\n", name );
+				MSG_Clear( &sv.multicast );
+				return;
+			}
+		}
+		else
+		{
+			Con_Printf( S_ERROR "MessageEnd: failed to rewrite message %s\n", name );
+			MSG_Clear( &sv.multicast );
+			return;
+		}
+	}
+
 	// check for system message
 	if( svgame.msg_index < 0 )
 	{
@@ -2662,9 +2751,7 @@ static void GAME_EXPORT pfnMessageEnd( void )
 	// update some messages in case their was format was changed and we want to keep backward compatibility
 	if( svgame.msg_index < 0 )
 	{
-		int	svc_msg = abs( svgame.msg_index );
-
-		if(( svc_msg == svc_finale || svc_msg == svc_cutscene ) && svgame.msg_realsize == 0 )
+		if(( svgame.msg_index == -svc_finale || svgame.msg_index == -svc_cutscene ) && svgame.msg_realsize == 0 )
 			MSG_WriteChar( &sv.multicast, 0 ); // write null string
 	}